RESEARCH· ·1970·

B198
GROUND-WATER RECHARGE
the basin probably is only a few inches thick, is considered
negligible. ~1oreover, numerous other complex
factors associated with flow through the zone of aeration
are deliberately disregarded and, as a result, the
term "apparent rate of movement" is used to describe
the observations considered in this report.
RESULTS AND COINCLUSIONS
Data for 38 storms were collected from June 1967 to
December 1968. Rainfall· during these storms ranged
from 0.18 to 3.99 inches. The time lag and apparent
rate of movement through the zone .of aeration for each
of the storms are listed in table 1. The time lag between
TABLE 1.-Time lag and apparent rate of movement of water through
the zone of aeration beneath a recharge basin on Long Island,
N.Y. ·
Date of storm
1967:
June 18 __________________ _
23 __________________ _
July 3--~---------------~
16 __________________ _
Aug.
25 24.~----------~------
__________________ _
25 __________________ _
28 __________________ _
30 __________________ _
5 __________________ _
9-------------------
25 10 __________________ ... ~~--------------_
25 __________________ _
26·------~~----------
27 _____ ~-------------
Oct. 18 ________ _..: __ :.. _____ 25 __________________ _
~ov. 23 __________________ _
25 __________________ _
I>ec. 3 __________________ _
1968:
~ar.
10--------------~--~-
11 __________________ _
28 __________________ _
23 __________________ _
Ap~ 24 __ ~-~--------------
June 12 __________________ _
19 __________________ _
July 24 27---------~---------
__________________ _
Aug. 1 __________________ _
Sept. 11 __________________ _
~ov. 7 __________________ 9 __________________ _
12 __________________ _
18 __________________ _
I>ec. 4 __________________ _
23 __________________ _
Average ______________ _
Apparent rate of
Time lag between movement through
inflow to basin and zone of aeration
initial water-table beneath the rerise
(hours) charge basin
(feet per hour)
12. 5 2. 8
14. 2 2. 5
8. 2 4. 2
7. 8 4. 5
3. 0 11. 7
7. 0 5. 0
3. 0 11. 7
3. 5 10. 0
6. 5 5. 4
7. 2 4. 8
8. 2 4. 2
10. 0 3. 5
9. 2 3. 8
4. 2 8. 2
11. 2 3. 1
6. 2 5. 6
4. 2 8. 2
6. 0 5. 8
8. 2 4. 2
13. 8 2. 5
11. 0 3. 2
11.5 3. 0
16. 5 2. 1
24. 0 1.5
11.0 3. 2
13. 8 2. 5
6. 0 5. 8
5. 8 6. 1
3. 5 10. 0
4. 5 7. 8
6. 0 5. 8
5. 0 7. 0
13. 0 2. 7
11. 0 3. 2
9. 0 3. 9
12.0 2. 9
10. 0 3. 5
14. 0 2. 5
9. 0. 5. 0
inflow to the basin and the initial rise of the water
table ranged from 3 to 24 hours and average~ 9 hours.
V aria.tions in the time lag appear to be -at least partly
related to antecedent soil-moisture conditions and to
the magnitude and intensity of rainfall. For example,
time lag seems to have been longer after comparatively
long periods of dry weather, and it seems to have been
shorter for high-intensity storms and for storms of
comparatively large magnitude. Presumably, soilmoisture
deficiencies decrease the apparent rate of
downward movement, and the higher hydraulic head
in the partly filled basin during larger storms or during
storms of high intensity increases the downward
rate of movement.
On the average, the time lag also seems to have increased
during the cold-weather months, perhaps because
of the greater viscosity of the water .. For example,
the average time lag for stor1ns during Noveinber
through ~1arch was 12.7 hours, and the a:verage
time lag for the warm-weather months, April through
October, was slightly more than 7 hours.
The computed average rate of apparent downward
movement through the zone of aeration is 5.0 feet per
hour for the 38 storms. The average rate during the
winter months is 3.0 feet per hour, and that during the
summer months is 6.0 feet per hour.
Even after intense storms or ones of long duration
and associated large amounts of inflow to the basin,
the basin floor commonly is dry within a few hours.
This fact also suggests that the infiltration rate and
the rate of movement in the zone of aeration are
moderately high.
Others (Isbister 1966, p. 49) have noted time lags of
downward movement through the zone of aeration on
Long Island ranging from less than 1 to more than 10
months. The average time lag noted by Isbister, in an
area where the depth to water is roughly comparable
to that beneath the basin described in the present report,
is 2-3 months. However, Isbister's observations
were made in an area underlain by glacial till of low
permeability, and the observations noted in this report
are believed to be more nearly representative of conditions
in areas underlain by the highly permeable
glacial outwash.
REFERENCES
Isbister, John, 1966, Geology and hydrology of northeastern
Nassau County, Long Island, N.Y.: U.S. Geol. Survey
Water-Supply Paper 1825, 89 p.
Seaburn, G. E., 1970, Preliminary results of hydrologic studies
at two recharge basins on Long Island, N.Y.: U.S. Geol.
Survey Prof. Paper 627-C, p.17.
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